1. Technical Field
The present disclosure relates to a support structure of a star wheel that prevents a sheet medium from lifting away from the platen surface, and to a printer having a star wheel.
2. Related Art
Inkjet printers that use star wheels having pointed tips formed at a regular pitch around the outside edge to prevent sheet media conveyed over the platen surface from lifting away from the platen surface are known from the literature. This type of printer is described in Japan Patent 4274180 and JP-A-2009-262544, for example.
The printer (an inkjet recording device) disclosed in Japan Patent 4274180 has spurs (star wheels) disposed on a head unit that carries a printhead group, and prevents media from lifting away from the conveyance belt by using the spurs (star wheels).
The printer disclosed in JP-A-2009-262544 includes spurs (star wheels) disposed on the housing of the printhead unit. The media is conveyed over a support member (platen) opposite the printhead unit. The roller surface of a drive roller is exposed at the surface of the support member, and the spurs (star wheels) are disposed at a position opposite the drive roller. The media is conveyed while pressed against the drive roller by the spurs (star wheels).
JP-A-H04-164766 discloses an image forming device (printer) having star wheels disposed so that they can roll on a movable shaft between levered support brackets. The support brackets can pivot up and down on a support shaft disposed at the top of the printer, but because there is a fixed arm that supports the movable shaft from below, the star wheels rise with the movable shaft and the conveyance path opens when the top of the printer is lifted up. When the top of the printer is closed, the tips of the star wheels contact the paper resting on the conveyance surface of the paper conveyance belt, and the paper is prevented from lifting up.
In line printers that have a printhead that is wider than the width of the recording paper and print with the printhead in a stationary position above the recording paper, the head unit that supports the printhead on the carriage is necessarily large. If the star wheels are mounted on the large head unit, the head unit becomes even larger, and the structure of the carriage that supports the printhead becomes more complicated. As the head unit becomes larger, the output of the carriage motor that drives the carriage must also be increased, further increasing cost. In addition, when the star wheels are mounted on the head unit, the star wheels also move when the head unit is retracted from above the platen. Keeping the star wheels always in the same place therefore may not be possible.
The conveyance path of the printer can be opened to remove paper jams and for other maintenance, for example. However, when printing is interrupted by a paper jam, for example, in a printer that holds the media depressed with star wheels, the star wheels may be exposed when the conveyance path is open. This can create problems, including interfering with removing paper jams and performing other maintenance tasks.
In the printer disclosed in JP-A-H04-164766, the star wheels are covered by the support brackets when the conveyance path is open. More specifically, because the movable shaft to which the star wheels are attached can move inside an oval hole formed in the support bracket, the support bracket descends of its own weight and moves to a position below the star wheels when the top unit opens. The star wheels can therefore be covered so they will not be touched.
However, while the configuration taught in JP-A-H04-164766 can prevent exposing the star wheels, the structure of the member (support bracket) covering the star wheels is complicated, and the configuration of parts is complicated. Furthermore, in this configuration, the angular position of the support bracket affects the pressure applied by the star wheels, and the pressure on the paper (media) may vary. Because variation in this pressure affects the paper conveyance load (media conveyance load), media conveyance precision may drop.